Should not happen again after 4 years ~~

it was random tests. fixed.

For any kata that includes random tests, you shouldn't be modifying the input array unless explicitly stated. So you know it's not a good idea, you did it anyway and then gave a below satisfaction rating?

Marking resolved.

You may have copy-pasted the wrong array. I've tested the array you pasted and it doesn't return null. Also, you didn't include the value n, but I tested the reference solution with n values of 10, 20, 60, and 100, and each returned ['Capulet', 30], ['Montague', 94], ['Montague', 160], and ['Montague', 227], respectively.

Created a fork that fixes according to your suggestion.

Waiting for the author to approve.

Spoiler!

Also fixed

You dont need to convert from Void to [()].
It is impossible to be in the Void case.

Oops, forgot to resolve the question

Hi, I had updated the example testcase.
In particular, what get you is
isLeft (substL isoEU (Right ())) shouldBe True

Removed again - late to the party ..

Please look at the function name carefully, it's prime77, not prime :)

?
I don't know your point.